Master paper for thermal page printer



United States Patent Office 3,519,464 MASTER PAPER FOR THERMAL PAGEPRINTER Lester Alfred Balster and Daniel Joseph Kay, Dayton,

Ohio, assignors to The National Cash Register Company, Dayton, Ohio, acorporation of Maryland No Drawing. Filed Mar, 1, 1967, Ser. No. 619,602Int. Cl. B41c 1/06; B41m 5/02 US. Cl. 117--36.1 1 Claim ABSTRACT OF THEDISCLOSURE The novel heat sensitive element of this invention comprisesa support, preferably a flexible backing such as paper, upon which iscoated at least one layer of a novel composition in a state of at leastpartial crystallization. In the state of at least partialcrystallization the composition is substantially nontacky, nonfluid, andsolid at room temperature. When heated to a temperature substantiallyelevated above room temperature, the heat sensitive novel coating ofthis invention undergoes a transition to an amorphous state andthereafter, for a substantial period of time, e.-g., twenty minutes,exhibits a tackifying state at a temperature substantially below theoriginal tacki fying temperature. Since only the image areas in theheat-sensitive layer are selectively heated by conductive heat transferto a temperature above the original tackifying temperature, only theimage areas of the heat-sensitive coating are activated. Afteractivation, the material in the image areas remain tacky atsubstantially lower temperatures while the unactivated background areasremain nontacky at this lower temperature.

The range of the components of the composition of this invention is setforth as follows:

Percentage by weight,

dryibasis (I) N-ethyl-p-toluene sulfonamide 50-70 (II) Glycerol ester ofhydrogenated rosin 5-10 (III) Chlorinated rubber 2.5-4 (1V) Diazo dye2-15 (V) Carbon black 1-10 (VI) Casein 1-5 (VII) Vinylacetate polymer,modified 6-12 (VIII) Sodium silicate 1-5 The present invention relatesto thermal printing ink. More specifically, this invention relates to athermal printing ink that provides a tacky, adhesive, transferable,colored material, that has the propery of remaining tacky when heated tothe tackifying temperature and remaining in a tacky state for aninterval of time after being cooled to a temperature less than thetackifying temperature.

The printing inks of the prior art encompass those such as set forth inLetters Patent No. 2,740,896 to Carl S. Miller on Apr. 3, 1956. Suchmethods require that heat-reducing radiation must fall on the printedcharacters of the document to be copied, which in turn produces avisible change in a heat-sensitive material coated upon a transparentcopying paper. In such methods very little of the radiation is absorbedand converted on the unprinted portions of the page, thus thetemperature does not increase at such unprinted areas and the copyingpaper remains unaffected. The printed portions of the page absorbradiation and by converting said radiation to heat results in anelevated-temperature pattern corresponding to the printed characters onthe document to be copied. Only a single copy is made therefrom.

The foregoing method is similar to that described in Letters Patent No.2,808,777 to Allen I. Roshkond, issued Oct. 8, 1957, which sets forththe manufacture of a du- 3,519,464 Patented July 7, 1970 plicatingmaster by positioning an original from which copies are desired to bemade in surface contact with a base sheet comprising a suflicientlycontinuous layer formed of material displacable at elevated temperaturesand then directed a sufficient quantity of radiation rich in infraredonto the original to generate a heat pattern and cause displacement ofthe heat displaceable material directly to the base sheet to form thecorresponding printing areas in the duplicating master.

Letters Patent No. 3,261,023 to William A. Light et al., which issued onJuly 12, 1966, shows a matrix comprising a sheet support having coatedthereon a layer of normally nontacky thermoplastic material at roomtemperature. The coating composition has the property of undergoingtransition from a partially crystalline state to a tacky amorphous stateat a temperature called the original tackifying temperature andremaining in said tacky state at a temperature below the originaltackifying temperature for at least long enough to permit transfer oftackified material from the matrix to produce a transfer print on areceiving surface at a transfer temperature below said originaltackifying temperature. That invention also requires that heat begenerated by infrared absorption by the printed characters of thedocument to be copied and that that heat be transmitted to an adjacentpolymer area on the matrix, raising the temperature of those areas abovethe original tackifying temperature of the polymer layer. The matrix isthen separated from the document to be copied and placed in contact witha receiving sheet. The method is limited to printed areas that areabsorbent of infrared radiation, which are distinguished from backgroundareas that are relatively nonabsorbent of infrared radiation. Theessence of the Light invention lies in the fact that a single matrix canbe activated thermographically more than one time, and after eachactivation a transfer print different from the last-imposedthermographic image can be made.

The persistent tacky state of an otherwise nontacky composition wasdisclosed in an adhesive in US. Pat. No. 2,462,029 to Lloyd M. Perry,which issued on Feb. 15, 1949, and has now expired. In that invention,particles of polymer material and a potential plasticizer therfor weremixed into a coating composition, which, when applied to paper, dried,and elevated in temperature, became tacky due to the solvent action ofthe plasticizer on the polymer material. Upon cooling, a slow reversiontook place in which the plasticizer crystallized.

A variation of the foregoing Perry composition is encompassed in US.Pat. No. 2,608,543, which issued on Aug. 26, 1952, to Charles M.Wiswell. The Wiswell composition included a ground-particle solideutectic polymer and a plasticizer. The Wiswell composition exhibited alower activating temperature range than the Perry composition. Neitherthe Perry patent nor the Wiswell patent made any disclosure of thetransfer of material from one sheet to another sheet, except thatnonimage-delineating transfer is inherent in sealing an adhesivematerial to a receptor surface.

The object of this invention is to provide a coating of heat absorbingmaterial ink on a sheet which can be heated other than by infraredradiation absorption in an image pattern, that is, by conduction, from anormally nontacky state to a tacky state, and which has the property ofremaining in a tacky state at temperatures substantially lower than thetemperature at which the ink composition originally reached a tackystate.

Another object of this invention is to provide an ink coating which willbe stratigraphically depleted of successive decrements of the adhesiveink.

Another object of this invention is to provide an ink 3 coatingcomposition in which no impact printing or radiation applicationpressures are required in making the original matrix or in making copiesfrom the matrix.

The preferred form of the instant invention has a paper sheet basecoated with a composition of distinctive color which qualifies it for amarking material. The composition of this invention being, substantiallysolid, nontacky, and nontransferable to another sheet in contacttherewith at room temperature, but which changes into a tacky-adhesive,contact-transferable state when heated to a temperature elevated aboveroom temperature, and which exhibits the property of remaining in astate having a tackifying temperature substantially lower than theoriginal tackifying temperature for at least long enough to permitsuccessive transfer of tackified material from the matrix thus formed toa plurality of transfer sheets.

The instant invention provides a solid phase transfer for reproductionof multiple copies from a single activation of the heat-sensitiveelement. The copies can be made on ordinary paper. The inventionprovides means by which a heat-sensitive matrix can be activated withthe support for the heat-sensitive layer in direct contact with aheat-conductive printing head or hot scriber, thus avoiding thermaldiffusion and obtaining a high resolution tacky image in theheat-sensitive layer. Copies can be made from the tacky layer after aninitial activation of the layer without need for further preferentialheating of the image areas during the sequential transferring steps ofthe process. The present invention provides for preparation of multiplecopies from a single heat-sensitive element of prints suitable forarchive use.

The prolonged tacky state at a temperature lower than the originaltackifying temperature after an initial activation is an idiosyncraticcharacteristic of the composition of this invention. It is accountedfor, partially, by delay of recrystallization after activation. Whilerecrystallization probably would occur, at least to some extent, inactivated unmixed amorphous materials, it is a characteristic of thecomposition of this invention that the rate of recrystallization attemperatures below the original tackifying temperature is sufficientlyslow that for a substantial period of time after activation theactivated material remains in a state having substantially the sametransfer characteristics as if the material were at temperature elevatedabove the tackifying temperature.

By tackifying temperature, as the term is used in the specification, ismeant the lowest temperature (or temperature range) at which thematerial in the state being described will become tacky. For acompletely crystallized thermoplastic polymer composition the tackifyingtemperature is the first order transition temperature; and for acompletely amorphous thermoplastic polymer composition the tackifyingtemperature is the second order transition temperature, sometimes calledglass transition temperature. In a composition that is partiallyamorphous and partially crystalline, the tackifying temperature will bea hybrid first order transition temperature and be somewhat below thetrue first order transition order temperature, the disparity between thetrue first order transition temperature and the hybrid first ordertransition temperature being dependent on the degree of crystallization.The term, tackifying temperature is used to denote both true first ordertransition temperatures, true second order transition temperatures, andvarying hybrids of the foregoing orders.

The instant invention does not pertain to infrared radiation,thermography, simultaneous printing material, light reflex printing,visible light patterns, free-standing patterns of tacky ink, the solventor drying principles of printing, or chemical action in the sense offorming colored material or the decoloration of the colored material.The matrix formed of the adhesive ink composition of this invention ispreferably heated by a thermal printing unit similar to that disclosedin US. Pat. No.

3,161,457 to H. Schroeder et al., which issued on Dec. 15, 1964. The inkcomposition can be heated by any printing member device which has anoutline or delineation of the data in terms of a temperature above thatof room temperature. Such printing members include relief surface,hot-type bodies, such as branding iron, thermographic plano-sheets, andtype bodies having a planar surface which is differentially heated.

The use of radiant heat is not only unnecessary in the practice of thisinvention, but is undesirable. In the particular printing member of theaforementioned Pat. No. 3,161,457, the planar surface is formed of theedges of stacked lamina of electrically-nonconducting material, eachlamina having one or more resistance supports on its edge. Selectivechoice of resistance on the laminae for electric energization willproduce a corresponding high-temperature pattern which, in contact withthe master sheet, will make a corresponding tacky pattern in thetransfer coating. An uncontrolled source of infrared radiation cannot beused in this process, and thermographically-formed patterns in acontrolled sheet will not usually have sufficient heat contentsatisfactorily to raise the temperature of the composition of thisinvention to its tackifying temperature. While this invention is aplanographic system, the planographic member which gives rise to thisdenomination is the master sheet and not the planographic printer head.

The tacky material in the activated areas of the heatsensitive layer hasan optical density and can be transferred seriatim by layers from theactivated areas to each of a plurality of receiving surfaces to producea plurality of images, produced seriatim.

The composition of this invention has the characteristic property ofremaining in a state of being tacky for a substantial time after oncebeing heated to the original tackifying temperature.

The preferred composition of this invention consists of the following:

Percentage by weight (dry basis) (I) N-ethyl-p-toluene sulfonamide 60.290 56.4 57. 51 (II) Glycerol ester of hydrogenated 59 00 rosin with asoftening point range of 88 C. and an acid number of 8.0 7 076 6. 7 6.77 7. 00 (III) Chlorinated rubber 3. 3. 3 3. 38 3. 48 (IV) Diazo dye 10.9 11.09 9.25 (V) Carbon black 7.6 7.71 5.72 (VI) Casein 0.750 2.1 2.09(VII) Vinylaeetate polymer, modified 9 730 9. 6 1). 73 9.60 (VIII)Sodium silicate 3. 540 3. 5 3. 44 3. 48 (IX) Surface active agent TraceTrace 0.18 (X) Defoaming agent Trace Trace 0.18

The range of the components of the composition of this invention is setforth as follows:

Percent by weight,

dry basis (I) N-ethyl-p-toluene sulfonamide 50-7O (II) Glycersol esterof hydrogenated rosin 5-10 (III) Chlorinated rubber 2.5-4 (IV) Diazo dye215 (V) Carbon black 1-10 (VI) Casein 1-5 (VII) Vinylacetate polymer6-12 (VIII) Sodium silicate 1-5 (I) N-ethyl-p-toluene sulfonamide actsas a plasticizer for the resins of the preferred composition. Thecompound exhibits a melting point of 58 C. and a boiling point of 340 C.(It is sold as Santicizer 3 by Monsanto Chemical Corporation, St. Louis,M0.) The molecular weight is 199.3; the density is 1.253 grams per cubiccentimeter; the specific gravity should range from 1.166 to 1.176; therefractive index should range from 1.512 to 1.532 at 65 C.; the vaporpressure should be 0.8 millimeter of mercury at C.

(II) The glycersol esters of hydrogenated wood rosins are predominantlymixtures of the glycerol esters of dihydroabietic acids. The degree ofsaturation should be greater than fifty percent of that theoreticallypossible,

The resin acids in wood rosin comprise approximately 30-37% abieticacid, 17% palustric acid, 2-13% neoabietic acid, 39% dehydroabieticacid, less than 2 percent levopimaric acid, 710% pimaric acid, 1014%isopimaric acid, as well as other homologues of abietic acid.

Since good color stability is desired, the glycersol ester of astabilized rosin, i.e. hydrogenated rosin, is used. Hy drogenation isone of the more satisfactory methods for decreasing the susceptibilityof rosin to air oxidation. A typical analysis for content of the varioustypes of acids in glycerol esters of hydrogenated wood rosins shows onlytwo changes from the unreduced form, viz, a decrease in thetwodouble-bond abietic-type acids from 53 to 3%, and an increase indihydroabietic acids from 11 to 60%; hence, the overall change isconversion of the former to the latter.

The chief effects of hydrogenation of rosins are to partially or totallyremove the double bonds present in the resin acids thus stabilizing theproduct, and to destroy color bodies found in natural wood rosins. Thedegree of saturation of glycersol esters of hydrogenated wood rosins isgreater than 50 percent of that theoretically possible, assuming thatthe resin acids found in wood rosin have an average of two double bonds,typical of which is abietic acid. As a result of hydrogenated woodrosins are dihydroabietic and tetrahydroabietic acids.

The glycerol ester of rosin, usually called ester gum, has decidedadvantages over both the raw material, rosin, and the metal-hardenedrosins with regard to durability, moisture resistance, and freedom fromlivering with basic pigments. Livering is a defect found in inks inwhich the pigments react chemically with vehicle constituents. It causesthe ink to body up and finally to gel completely. The composition ofthis invention shows no evidence of livering.

The ester gum of optimum physical properties is that in which threemoles of resin acids combine with one mode of glycerol to produceglycerol triabietate. Commercial ester gum is composed of both themonoand the diglycerides as well as the completely esterified product.Unreacted glycerol in the finished product is to be avoided if an esterof proper hardness and water resistance is to be obtained. A suitableester gum, with acid number 5-10, is produced by heating rosin withglycerol at 250 C. The reaction can be carried to completion at 290 C.in a vessel provided for the removal of the water produced. The glycerolester of hydrogenated rosin should exhibit medium relative viscosity,negligible odor, good oxidation resistance and only slight coloration.(The mixture is sold as Staybelite Ester No. 10 by the Hercules PowderCompany, Wilmington, Del.)

(-III) The chlorinated natural rubber used in the composition of thisinvention is the product of the chlorination of polyisoprene rubber andacts as a tackifier. It is odorless and shows excellent clarity in filmform. The chlorination of natural rubber which is a polymer made up ofisoprene units, takes place in a complex fashion with addition andsubstitution of chlorine occurring as well as cyclization along thepolymer chains and the cleavage of the polymer chains into shorterchains. The chlorination process terminates when the unsaturatedcharacteristics of the rubber have been exhausted. The chlorine contentis approximately 67% and is great enough to insure an optimum ofstability, compatibility and resistance to fire. The viscosity of thechlorinated rubber ranges from 9 to 14 centipoises. (The chlorinatedrubber of the preferred embodiment of this invention is sold as Parlon10 by the Hercules Powder Company, Wilmington, Del., U.S.A.)

(IV) The diazo dye of the preferred embodiment is Oil Black ET (forexample, that sold by Allied Chemical and Dye Corporation). The dye usedin the composition is of the diazo type such as that having a ColorIndex No. 26150. The preferred dye does not exclude compositionsembodying other dyes such as aryl amine dyes having Color Index Nos.26200, 26210, 26270, 26300, 26315, 26330, 26380, 26405, 26750, and26950.

Other suitable coloring addenda include the following materialsavailable from the Allied Chemical and Dye Corporation: Azo Oil Black,Alizarin Blue G.R.L. Base, Oil Scarlet 60, Oil Red G.R.O., Oil Red 0,Oil Orange 2311, Plasto Oil M.G.S., Insol Black Ultra Blue 9775A, andA20 Oil Blue Black B. Other coloring addenda include Nile BlueHydroxide, Methyl Red, Prussian Blue Pigment, Iron Oxide, Peacock Blue,Phloxine, Chrome Yellows, etc.

(V) Carbon blacks are usually prepared by the impingement of smallnatural gas flames. They consist chiefly of 88.4% carbon with 0.4%hydrogen and 11.2% oxygen. Any of the 25 grades of manufactured carbonblack can be used in this invention such as that sold by SterlingChemical Co. as Grade R.

(VI) The lactic acid casein (sold as Casein FF-30 by The Borden Co., NewYork, N.Y., U.S.A.), was modified especially to be low foaming and isused as a film forming transfer regulator.

Preparation methods for acid precipitation of casein are set forth inU.S. Pat. No. 1,716,799 which issued June 11, 1929, to W. H. Sheffield;U.S. Pat. No. 1,892,233, which issued Dec. 27, 1932, to F. L. Chappell;U.S. Pat. No. 1,992,002, which issued Feb. 19, 1935, to F. L. Chappell;U.S. Pat. No. 2,044,282, which issued June 16, 1936, to F. H. Clickner.The precipitating acid may be lactic, sulfuric, or hydrochloric.

Commercial acid casein is obtained from skim milk by selectiveprecipitation with lactic acid and whey removal. Solutions of acidcasein are prepared by soaking casein in water and subsequently addingalkali and heating and stirring at 4050 C. The minimum quantities ofalkalies required for dissolving acid casein (in parts per 100 parts ofcasein) are as follows: 3% sodium hydroxide; 3% ammonium hydroxide; 5%sodium carbonate; 12% sodium phosphate, and 15% sodium bromate or sodiumborate. Alkaline solutions of casein form continuous films on drying.Commercial acid casein is about 84% pure casein. The principalnonprotein materials, besides moisture, are ash constituents (largelycalcium phosphate) lactose, and fat.

Preservatives for casein include phenols, chlorophenols, 2-naphthol,benzoates and salicylates.

Pine oil can be used as a combined preservative, wetting agent(surfactant), and defoamer.

(VII) The vinyl acetate polymer (sold as Gelva C5- V16R by MonsantoChemical Corp., St. Louis, Mo.), modified to be soluble in ammoniumhydroxide solution, exhibits a softening point of 134 C. and a viscosityof 13-18 cps. in a concentration of 86 gm./1000 cubic centimeters ofethyl alcohol at 20 C., using an Ostwald viscometer. It is used as a hotmelting adhesive. The preparation of the vinyl acetate polymer is setforth in U.S. Pat. No. 2,412,239 which issued Dec. 24, 1946, to G. I.Manson; U.S. Pat. No. 2,486,855 which issued Nov. 1, 1942, to E. Lavinand C. L. Boyce; U.S. Pat. No. 2,435,- 909 (Reissue No. 23,164, Nov. 1,1947) to N. G. Tompkins, and U.S. Pats. Nos. 2,508,341 and 2,508,343which issued May 16, 1950, to W. K. Wilson.

(VIII) The sodium silicate used in this invention exhibits a weightratio of silicon dioxide to sodium oxide of 2.5 to 3.4; the percentageof sodium oxide can range from 5 to 20; the percentage of silicondioxide can range from 20 to 40; the viscosity at 68 F. can range fromcentipoises to 1,000 centipoises. The chemical formula is Na O.xSiOwhere x ranges from 3 to 6.

(IX) The gross effects of surface-active compounds are styled asdetergency, wetting, foaming, dispersion, and emulsification. Thesurfactants or wetting agents of the 7 preferred embodiment of thisinvention are alkylaryl polyether alcohols such asisooctylphenoxyethanol (sold as Triton N100 by Rohm & Haas Company,Philadelphia, Pa., U.S.A.).

Among the other surfactants which can be used in this invention are:Sodium alkylnaphthalenesulfonate (sold as Alkanol B by the Du PontCorporation, Wilmington, Del., U.S.A.); sodium cetylsulfate (sold asAvitex SF by the Du Pont Corporation of Wilmington, Del); sodium oleylsulfate (sold as Duponol LS by the Du Pont Corporation of Wilmington,Del., U.S.A.); sodium N- methyl-N-oleyltaurate (sold as Igepon T byGeneral Aniline Film Corporation of New York, N.Y.); sodiumoleylisethionate (sold as Igepon A by General Aniline Film Corporationof New York, N.Y.); sodium dodecyl benzenesulfonate (sold as SantomerseNo. 1 by the Monsanto Chemical Corp., St. Louis, Mo.); sorbitanmonopalmitate (sold as Span 40 by the Atlas Powder Company, Wilmington,Del);

(sold as Tergitol 08 by Union Carbide Corporation, New York, N.Y.);

(sold as Triton W-30 by Rohm & Haas Co., Philadelphia, Pa); PC H C H(OCH CH ),,OI-I (sold as Triton X-100 by Rohm & Haas Co., Philadelphia,Pa.

(X) The silicone defoamer used in the preferred composition of thisinvention is sold by Nopco Chemical Co., Newark, N.J., as Nopco NDW. Itis a dark yellow liquid silicone having a minimum of 0.5% moisturecontent and a specific gravity range of 0.87 to 0.91.

Some of the most effective antifoam agents are among the dimethylsilicones. Minimum concentrations of 9 parts per million are effectivein the practice of this invention. The dimethyl silicone fluids areobtainable from the Dow Corning Corporation under the trade designation200 Fluids, from the General Electric Co., Silicone Products Division.

Other foam preventing agents which can be used in the practice of thisinvention include Z-ethylhexanol, frequently referred to as octylalcohol; diisobutylcarbinol (2,6-dimethyl-4-heptanol). Additionalantifoaming agents are fatty acids and fatty acid esters such as thoseset forth in US. Pat. No. 2,304,304, which issued on Dec. 8, 1942, andin US. Pat. No. 2,390,212, which issued on Dec. 4, 1945, both to J. H.Fritz; pine oil, alkyl lactates; higher ethers such asZ-(di-tert-amylphenoxy) ethanol, as set forth in US. Pat. No. 2,407,589,which issued on Sept. 10, 1946, and US. Pats. Nos. 2,453,351 and2,453,352, which issued Nov. 9, 1948, to H. E. Tremain and L. R. Bacon;organic phosphates and metallic soaps.

The heat-sensitive element of this invention comprises a heat-sensitivecoatable composition containing at least two specific polymericcomponents coated on a suitable support by a well-known manner, such asextrusion, hopper coating, dip coating, doctor blade coating, etc.Suitable supports include paper, e.g., 8 pound (20 x 30/480) Tuscan WSGrade from the Peter J. Schweitzer Division of the Kimberly ClarkCorporation; glassine, vegetable parchment; film base, e.g., celluloseacetate butyrate, cellulose acetate propionate, etc.; polyester filmbase, e.g., polyethylene terephthalate, etc.

To the polymer-containing composition can be added addenda to accomplisha variety of purposes, such as agents to modify the flexibility of thelayer, to modify the surface characteristics, to impart color to thelayer; to modify the adhesivity of the heat sensitive layer to itssupport; other plasticizers, tackifiers, and surfactants. A variety ofdyes may be added to achieve specific colors.

Water is an excellent dispersing medium for the components of thisinvention.

The above addenda may, without affecting crystallization, havebeneficial effects to both surfaces of the heat-sensitive layer, forexample, increasing its adhesion to its support; while on the surfacefacilitating intimate contact between the coating layer and the copypaper document during transfer of the coating, at the same timepreventing optical contact.

In preparing the heat-sensitive elements according to the invention, asingle coating of the polymeric coating composition is normally appliedto the support at a thickness to give a predetermined thickness whendried. Alternatively, the coating layer can be built up of two or threecoats. The dry thickness of the heat-sensitive layer can vary over awide range. For example, a suitable coating thickness can be in a rangeof about 0.05 to about 5.0 mils. A preferred coating thickness is foundto be in a range of about 0.10 to about 3.0 mils.

The preferred method for activating heat areas of the heat-sensitivecoating, as noted supra, is to contact the heat-sensitive coating with aprinting element such as that described in US. Pat. No. 3,161,457, whichissued on the application of Hans Schroeder et al., on Dec. 15, 1964,and in which high-temperature images of selected configuration can bemade in an otherwise substantially planar cool surface of the typemember. In the embrace of the concept of the invention there may besupplied for the hot pattern for the impression means of the mastersheet hot letter press type, hot scribers, or any pattern source of allheat which may be pressed into the master sheet. An uncontrolled sourceof infrared radia tion cannot be used in this system sincethermographically-formed patterns in a control sheet, generally, willnot have sufiicient heat content to work satisfactorily with the mastersheet coating contemplated by this invention.

EXAMPLE I A heat-sensitive element of the instant invention was preparedas follows: 17 grams of N-ethyl-p-toluene sulfonamide, 2 grams of theglycerol ester of hydrogenated rosin, 1 gram of chlorinated rubber, 2grams of Oil Black BT dye, and 1 gram of carbon black were mixedtogether, heated until a homogeneous dispersion was formed at atemperature of approximately 60 C. The dispersion was recrystallizedupon a lowering of the temperature.

To 20 grams of the mixture prepared supra was added 42.7 grams of a 15%solution of polyvinylacetate in ammonia solution, 10 grams of water, 1drop of isooctylphenoxyethanol, and 1 drop of dimethyl siliconeantifoaming agent. The composition mixture was ground in an attritoruntil the particle size was homogeneous. After thoroughly mixing theabove composition while holding it at a temperature of about 25 C., thecomposition was doctor blade coated onto a sheet of base paperconsisting of 8 lb. (20 x 30/480) Tuscan WS Grade from the Peter J.Schweitzer Division of the Kimberly Clark Corporation at a thicknesssuch as the dry coating weight was approximately 13 lbs. per ream, 25 x38/500 (3300 sq. ft.). The coating was then dried to remove the waterand calendered to give a fiat, smooth surface. The finished product wasexposed to a printing head of the type set forth in US. Pat. No.3,161,457, to H. Schroeder et al., which issued on Dec. 15, 1964. Theink-containing coating was heated by said printing member causing thelayer to become tackified in those areas corresponding to the characterareas of the printing head. The heat-sensitive element while retainingits tacky state was exposed to copy sheets of paper, supported byrollers. The transfer of tacky material produced a good blackblueproduction of a pattern on the copy paper. The transfer step wasrepeated several times on several copy sheets from a single activationof the heat-sensitive coating.

EXAMPLE II 595 grams of N-ethyl-p-toluene sulfonamide, 70 grams of theglycerol ester of hydrogenated rosin, 35 grams of chlorinated rubber, 70grams of Oil Black BT dye, and 35 grams of carbon black were mixedtogether, heated until a homogeneous dispers on was formed at atemperature of approximately 60 C. The material was at least partiallyrecrystallized upon a lowering of temperature.

To 18 grams of the above composition was added 1 gram of Oil Black ET, 1gram of carbon black, grams of a 15% solution of polyvinylacetatecopolymer in ammonia solution, 15 grams of water, 2.1 grams of sodiumsilicate in alkaline solution, 1 drop of dimethyl silicone defoarner,and 1 drop of isooctylphenoxyethanol. The composition mixture was groundin an attritor until the particle size was homogeneous. After thoroughlymixing the above composition While holding it at a temperature of 25 C.,the composition was doctor blade coated onto a sheet of base paperconsisting of 8 lb. x 30/480) Tuscan WS Grade from the Peter J.Schweitzer Division of the Kimberly Clark Corporation at a thicknesssuch as the dry coating weight was approximately 13 lbs. per ream, x38/500 (3300 sq. ft.). The coating was then dried to remove moisture andcalendered. The finished product was exposed to a printing head of thetype set forth in US. Pat. No. 3,161,457 to H. Schroeder et al., whichissued on Dec. 15, 1964. The ink-containing coating was heated from theback (uncoated) side by said printing member causing the layer to becometackified in those areas corresponding to the character areas of theprinting head. The heat-sensitive element While retaining its tackystate was exposed to copy sheets of paper supported by rollers. Thetransfer of tacky material produced a good black-blue production of apattern on the copy paper. The transfer step was repeated several timeson several copy sheets from a single activation of the heat-sensitivecoating.

EXAMPLE III 26.6 grams of N-ethyl-p-toluene sulfonamide, 3.14 grams ofthe glycerol ester of hydrogenated wood rosin, 1.56 grams of chlorinatedrubber, 4.14 grams of Oil Black BT dye, and 2.56 grams of carbon blackwere mixed together and heated until a homogeneous dispersion formed ata temperature of approximately 60 C. The components were recrystallizedby lowering the temperature of the dispersion.

To 20.0 grams of the above composition was added: 15.0 grams of a 15%solution of polyvinylacetate copolymer in ammonium hydroxide; 15.0 gramsof water, 2.1grams of a 38% solution of sodium silicate in sodiumhydroxide, 1 drop of 2,4,7,9-tetramethyl-5-decyne-4,7- diol, and 1 dropof a dimethylsilicone antifoaming agent. The foregoing mixture wasground in an attritor until the composition exhibited a homogeneousparticle size. After thoroughly mixing the above composition whileholding it at a temperature of 25 C., the composition was doctor bladecoated onto a sheet of base paper consisting of 8 lb. (20 x /480) TuscanWS Grade from the Peter J. Schweitzer Division of the Kimberly ClarkCorporation at a thickness such as the dry coating weight wasapproximately 13 lbs. per ream, 25 x 38/500 (3300 sq. ft.). The coatingwas then dried to remove the water and calendered. The finished productwas exposed to a printing head of the type set forth in US. Pat. No.3,161,457 to H. Schroeder et al., which issued on Dec. 15, 1964. Theink-containing coating was heated by said printing member causing thelayer to become tackified in those areas corresponding to the characterareas on the printing head. The heat-sensitive element while retainingits tacky state was exposed to copy sheets of highly absorbent sheetpaper supported by rollers. The transfer of tacky material produced agood black-blue production of a pattern on the copy paper. The transferstep was repeated several times on several copy sheets from a singleactivation of the heat-sensitive coating.

EXAMPLE IV The heat-sensitive composition of the present invention wasprepared as follows: 42.7 pounds of N-ethyLp'tOluene sulfonamide, 5.02pounds of the glycerol ester of hydrogenated rosin, 2.51 pounds ofchlorinated rubber, 6.65 pounds of Oil Black BT dye, and 4.12 pounds ofcarbon black were mixed together and heated until a homogeneousdispersion formed at circa 60 C. The composition was then cooled until astate of at least partial crystallization was achieved. To the foregoingwas added 1.5 pounds dry of casein in solution and 6.9 pounds of a 15solution of polyvinylacetate copolymer in ammonium hydroxide solution,and 2.5 pounds of a 32% solution of sodium silicate. The mixture wasground in an attritor until the particle size was homogeneously small.

Some of the advantages of the present invention have been described inthe foregoing part of the specification. Many others are apparent. Forexample, the elements produced by the present invention are permanent instorage; the heat-sensitive layers are unusually resistant to wear,abrasion, crackling, etc. The process in which the elements are employedare normally completely dry, thus not requiring chemicals, solvents andthe like. Moreover, the process for copies reproduced do not require astabilizing step. The copies produced by process of the invention arepermanent and are not affected by high temperature or humidity. Thecopies are ideally suited for archival storage for these reasons. Sincehigh resolution and high quality are obtained in the copies, they arealso acceptable for use in the fields of industry and commerce.

What is claimed is:

1. A heat-sensitive element for use in a thermal printing process usinghot printing members in heat-conductive contact with the element, saidelement comprising a support of paper, a heat-sensitive layer of athermoplastic composition coated on said support, said compositioncomprising at least three organic filming materials capable of at leastpartial crystallization, said film-forming materials comprising at leastone organic acid ester, and at least one modified vinyl acetate polymer;a tackifier for said film-forming materials, at least one plasticizerfor said film-forming materials; at least one organic dye; carbon blackparticles; and at least one alkali metal silicate; said compositionhaving an original tackifying temperature, at which temperature saidcomposition will undergo transition from a state of at least partialcrystallinity to an amorphous state, said composition having theproperty of remaining for a substantial period of time after saidtransition to the amorphous state at a temperature substantially belowsaid original tackifying temperature, wherein said organic film-formingmaterials comprise from 12 to 27%, by weight, of said composition; saidtackifier comprises from 2.5 to 4%, by Weight, of said composition; saidplasticizer comprises from 50 to 70%, by weight, of the saidcomposition, and wherein said organic dyes comprise from 2 to 15 byweight, of said composition, all weights being on a dry basis; andWherein the plasticizer is N-ethyl-p-toluene sulfonarnide, the organicacid ester is glycerol ester of hydrogenated rosin, the tackifier ischlorinated rubber, the vinyl acetate polymer is modified bycarboxylation until soluble in ammonium hydroxide, and the metalsilicate is sodium silicate.

References Cited UNITED STATES PATENTS 2,462,029 2/ 1949 Perry.

2,678,284 5/1954 Holt.

2,885,307 5/1959 Rigterink et al.

3,117,100 l/1964 Cox et a1. 260-27 3,260,612 7/1966 Dulmage et al11736.1 3,261,023 7/1966 Light et a1. 1l736.1 3,342,623 9/1967 Dulmageet a1. 117--36.1

MURRAY KATZ, Primary Examiner US. Cl. X.R.

l01470, 473; ll7l38.8, 26027 UNITED STATES RATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,519,464 July 7, 1970 Lester Alfred Balster eta1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as, shown below:

Column 1, line 58, "heat-reducing" should read heatinducing Column 3,line 1, after "printing" insert pressures line 2, "application" shouldread applications same line 2, cancel "pressures".

Signed and sealed this 16th day of February 1971.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, J R.

Attesting Officer Commissioner of Patents

